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CDC's Walenksy explains the new 5-day COVID isolation advisory, Omicron severity to Stephen Colbert

Stephen Colbert had Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention (CDC), on Monday's Late Show, and he began by asking her about the state of the COVID-19 pandemic, and specifically about the severity of the new Omicron variant.

Omicron is two to three times more transmissible than Delta, Walensky said, but it does "seem to be a little bit less severe in any given individual." Colbert was curious about the word "seem," and Walensky said U.S. public health officials are going mostly off of data from South Africa and Britain, where hospitalization rates and deaths "did not rise as much as they've seen in prior waves," and lengths of hospital stays are shorter.

South Africa's situation is different than America's, Walensky conceded, "but we're starting to see similar things here," with a modest increase in hospitalizations even as case numbers surge. We'll see the effects of Christmas and New Year's gatherings in a week or two, she added.

"The big CDC news," Colbert said, is that "y'all have now gone from recommending a 10-day isolation to a five-day isolation. Why the change?" Walensky said from the past two years we know that "probably about 80 to 90 percent of your transmissibility has happened in those first five days," right before and right after you have symptoms, "and we really want people to be sure if they're gonna be home, they're going to be home for the right period of time, when they're maximally transmissible."

The U.K. advises a negative test before you leave quarantine, and on Sunday, Dr. Anthony Fauci "suggested that's under consideration" here, Colbert said. "Is he talking out both sides of his mouth over there and you'd like to tell him, 'Put a cork in it, Tony'?" Walkensky laughed and said no. The rapid antigen tests are approved mostly for early detection, she said, and whether or not you test negative at the end of the five-day period, "you still should probably not visit grandma, you shouldn't get on an airplane, and you should still be pretty careful when you're with other people by wearing your mask all the time." If you can't do that — Colbert, for example, said he wouldn't wear a mask during his monologue — you should still isolate for 10 days, Walensky said.

Colbert ended the interview by asking Walensky about the lack of rapid antigen tests and how the CDC plans to restore credibility that was sapped during the Trump administration.